PMDF User's Guide
OpenVMS Edition

Messages which contain 7-bit or 8-bit control characters can cause problems when they are displayed, if those control characters are treated as commands to the terminal. Such control characters can be filtered out by using the /FILTER_CTRL qualifier on the PMDF MAIL command when an interactive session is started. This qualifier can also be specified on any individual command which displays a message (such as READ or NEXT ). When filtering is turned on, each control character will be replaced by a text representation of its hexidecimal value, in the format "=XX".

Be aware that if a message has been read with filtering, the filtered version of the text is what will be used for any further operations, such as FORWARD , REPLY , EXTRACT , or PRINT . To use the original version instead, reread the message with /NOFILTER_CTRL. Or better, read it with /NOMIME/NOFILTER_CTRL which prevents PMDF MAIL from parsing out and decoding the original MIME structure of the message at all.